1. Field of the Invention
The present invention is in the field of hydroxyl-containing polymers prepared from alpha, beta-ethylenically unsaturated monomers, and more particularly, to low molecular weight polymers prepared from reacting alpha, beta-ethylenically unsaturated acids and epoxy compounds.
2. Brief Description of the Prior Art
High solids or low organic solvent-containing compositions are becoming increasingly important in the coatings industry because state and local governments are requiring low solvent emission from the coatings. To achieve the necessary high solids content, the resinous binder is usually a low molecular weight polymer. Such polymers ahve relatively fliud viscosities enabling them to be formulated withlow amounts or even no organic solvent and yet still have the flowability necessary for good coating application properties. Unfortunately, coatings prepared form low molecular weight polymers often have poor physical and chemical properties. This is particularly the situation with regard to thermosetting acrylic coating compositions prepared from low molecular weight hydroxyl-functional copolymers and curing agents such as aminoplast resins. Although not intending to be bound by any theory, it is believed that because of the relatively high reactivity of the hydroxyl-containing acrylic monomers in comparison with the non-functional acrylic monomers, many of the polymer chains do not contain hydroxyl functionality. As a result, these non-functional polymer species are weak links in the cured coating since they do not contain sites for crosslinking.
Although it would be possible in principle to prepare polymers from only hydroxyl-containing monomers such as hydroxypropyl acrylate and hydroxyethyl methacrylate, thus assuring that every polymer would contain hydroxyl functionality, in practice it is not possible to do so. Such polymers are not useful in industrial coatings application because of their limited solubility and their hydrophilicity. They are simply too sensitive to humidity to be useful for many industrial coating applications.